There is an ever-increasing need for air handling systems that include air filtration systems that can protect an enclosure against noxious airborne vapors and particulates released in the vicinity of the enclosure. Every year there are numerous incidents of noxious vapors contaminating building environments and causing illness and disruptions. There is also a current effort to protect buildings and other significant enclosures against toxic airborne vapors and particulates being released as part of terrorist acts. As a result, new filter performance requirements have been promoted by the United States government and regulatory agencies to protect against certain toxic gases. Whether in a civilian or military setting, a typical air filtration system that contains only a particulate filter (for example, a cardboard framed fiberglass matt filter) provides no protection at all against toxic vapors. Commercially available electrostatic fiber filters exhibit higher removal efficiencies for smaller particles than standard dust filters, but they have no vapor filtration capability. HEPA (“High-Efficiency Particulate Air”) filters are used for high-efficiency filtration of airborne dispersions of ultrafine solid and liquid particulates such as dust and pollen, radioactive particle contaminants, and aerosols. However, where the threat is a gaseous chemical compound or a gaseous particle of extremely small size (i.e., <0.001 microns), the conventional commercially-available HEPA filters cannot intercept and control those types of airborne agents.
The most commonly used filter technology to remove vapors and gases from contaminated air is activated carbon. Such carbon-based gas filtration has been implemented in a wide variety of vapor-phase filtration applications including individual gas masks as well as vehicle and shelter protection. In these applications, activated carbon can be impregnated with metal salts to remove a full range of toxic vapors (such as VOCs, arsine, Sarin gas, etc.). These toxic gases require a high filtration efficiency typically not needed for most commercial applications. To the contrary, typical commercial filters generally include activated carbon materials on or incorporated within non-woven fabrics (fiber mats, for instance), with coexisting large fixed beds of packed adsorbent particles. Such commercial filters used for air purification generally are used until an easily measurable percentage (e.g., 10%) of the challenge chemical(s) concentration is measured in the effluent. Much greater efficiencies (e.g., 0.001%) are desired for military gas masks and collective protection applications (such as vehicles, mobile shelters, and fixed sites).
Impregnated, activated carbons are used in applications where it is required to remove gases that would not otherwise be removed through the use of unimpregnated activated carbons. Such prior art impregnated carbon formulations often contain copper, zinc, molybdenum, silver, and sometimes chromium impregnated on an activated carbon. These adsorbents are effective in removing a large number of toxic materials, such as cyanide-based gases and vapors.
In addition to a number of other inorganic materials, which have been impregnated on activated carbon, various organic impregnates have been found useful in military applications for the removal of cyanogen chloride. Examples of these include triethylenediamine (TEDA) and pyridine-4-carboxylic acid.
Various types of high-efficiency filter systems, both commercial and military types, have been proposed for building protection using copper-silver-zinc-molybdenum-triethylenediamine impregnated carbon for filtering a broad range of toxic chemical vapors and gases. However, such specific carbon-based filters have proven ineffective for other gases, such as, ammonia, ethylene oxide, formaldehyde, and nitrogen oxides. As these gases are quite prominent in industry and can be harmful to humans when present in sufficient amounts (particularly within enclosed spaces), and, to date, other filter devices have proven unsuitable for environmental treatment and/or removal thereof, there exists a definite need for a filter mechanism to remedy these deficiencies. This has proven very difficult to provide a filter medium that effectively removes all such noxious gases simultaneously. Of particular difficulty is the ability to remove such disparate gases in a wide range of relative humidity environments. Each gas is affected differently by adsorbed water. For ammonia, it is typically most difficult (design limiting) to filter at a low relative humidity since adsorbed water can enhance the ammonia affinity of the target adsorbents. For ethylene oxide the reverse is true since exposure to high humidity and the commensurate increase in adsorbed water, is problematic in designing a proper filter system. To date, no filtration system having a relatively small amount of filter medium present has been provided that effectively removes all such gases simultaneously for long durations of time at relatively high challenge concentrations (e.g., 1,000 ppm) without eventually eluting through the filter.
It has been realized that silica-based compositions make excellent gas filter media. However, little has been provided within the pertinent prior art that concerns the ability to provide uptake and breakthrough levels by such filter media on a permanent basis and at levels that are acceptable for large-scale usage. Uptake basically is a measure of the ability of the filter medium to capture a certain volume of the subject gas in a short period of time (fast mass transfer); breakthrough is an indication of the loss of usefulness of the filter medium (a combination of capture and filter medium equilibrium capacity). Thus, it is highly desirable to find a proper filter medium that exhibits a high uptake (and thus quick capture of large amounts of noxious gases) and long breakthrough times (and thus, coupled with uptake, the ability to not only effectuate quick capture but also extensive lengths of time to reach the filter capacity). The standard filters in use today are limited for noxious gases, such as ammonia, to relatively quick breakthrough times, caused by slow uptake and/or low filter capacity. There is a need to develop a new filter medium that increases uptake and breakthrough, as a result.
The closest art concerning the removal of gases such as ammonia utilizing a potential silica-based compound doped with a metal is taught within WO 00/40324 to Kemira Agro Oy. Such a system, however, is primarily concerned with providing a filter media that permits regeneration of the collected gases, presumably for further utilization, rather than permanent removal from the atmosphere. Such an ability to easily regenerate (i.e., permit release of captured gases) such toxic gases through increases of temperature or changes in pressure unfortunately presents a risk to the subject environment. To the contrary, an advantage of a system as now proposed is to provide effective long-duration breakthrough (thus indicating thorough and effective removal of unwanted gases in substantially their entirety from a subject space over time), as well as thorough and effective uptake of substantially all such gases as indicated by an uptake measurement. The Kemira reference also is concerned specifically with providing a dry mixture of silica and metal (in particular copper I salts, ultimately), which, as noted within the reference, provides the effective uptake and regenerative capacity sought rather than permanent and effective gas (such as ammonia) removal from the subject environment. The details of the inventive filter media are discussed in greater depth below.
Additionally, ethylene oxide (“EO”) is a highly toxic substance found in various locations as a gas. Stringent governmental guidelines have been developed in an effort to protect workers present within a potentially EO-contaminated environment. The closest art concerning the utilization of zeolites for ethylene oxide modification through dehydration of such a compound to different, harmless, or less harmful, species, is found within U.S. Pat. No. 4,306,106 to Kerr et al. The utilization of impregnated zeolites for EO removal from airstreams is disclosed within U.S. Pat. No. 6,837,917 to Karwacki et al. However, there is no discussion of the availability of such materials in combination with any other compounds for the simultaneous and effective removal of differing noxious gases from certain environments within either of these publications.